This invention relates to highly reliable power supplies and more specifically to highly reliable board mounted power modules.
As a result of the increasing scale of integration which has been encountered during the past decades, a very large amount of circuitry can be mounted on a single circuit board. The amount of this circuitry is so great that every effort must be made to avoid a failure of a circuit board. As an example of a circuit board which contains a large body of critical circuitry, there is the case of a circuit board used as an interface for DS3 signals in a telecommunications network using digital (pulse code modulation) signals. This single board interfaces 672 voice channels. The loss of all these channels is, of course, highly undesirable.
A major weak link in any such circuit board is the power supply. Typically, each such board has its own power supply driven from a single battery source.
In the prior art, the most common arrangement for providing this highly reliable power is to have two separate power supplies and to simply parallel their outputs. If one power supply fails, power is still provided from the other supply. This is expensive in material cost and in board area. This arrangement has been used, for example, in the above-mentioned board for interfacing with DS3 signals in the No. 4ESS(copyright) formerly manufactured by Lucent Technologies Inc.
To provide fault isolation, diodes may be inserted between the two power supplies and the load. A problem with this arrangement is that it is very difficult to detect diode failures, and it is therefore a source of potential problem if other failures occur. This particular problem has been solved in accordance with the teachings of U.S. Pat. 6,157,308 which places the isolating diodes in close proximity to a controllable heater source and observing the voltage across the diode when the diode is heated.
Another problem related to diodes is that the two power system""s return currents can intermix, causing potential isolation issues which in turn can reduce system reliability.
Both of the above arrangements are expensive and still have the disadvantage that problems in one of the duplicated power supplies cannot be fully isolated from the other power supply and can cause the board to fail.
The above problems are essentially solved and an advance is made over the teachings of the prior art in accordance with this invention wherein redundancy is introduced into a single power supply by duplicating the input power train of one power supply and feeding each of the duplicated power trains to two separate primary windings of a three winding transformer. The secondary (or third winding) of the transformer is then connected to the output power train.
Advantageously, this arrangement fully isolates the two input power trains of the power supply from each other (since they are connected to separate windings of the power transformer) and requires only a single output power train.
Advantageously, this arrangement costs only about 30 percent more than a single power supply and is therefore much less expensive than a pair of power supplies provided for duplication and isolation purposes.
Advantageously, redundancy is achieved without the use of diodes and at the same time the arrangement offers superb fault isolation capabilities.
In accordance with Applicants"" preferred embodiment, the power supply is controlled by a program controlled controller. This controller provides a pair of signals, one for each of the input power trains, to control the amount of energy that each input power train supplies to the primaries of the transformer. The controller can be arranged to have the power supply draw all input current from only one of the input power trains connected to one of the battery distribution systems. This is desirable if one of the input power sources fails or is removed from service for maintenance. In case a unit has been placed in the maintenance mode and there is a failure in the power system currently driving that unit, then the controller can automatically revert to a state in which the non-failing power distribution system is used.
The controller can also be arranged to draw equal energy from each of the input power trains; this mode of operation increases the lifetime of the power supply since then under normal conditions, each single power supply is operating at 50% loading capacity. In equal energy mode, the current drawn from each power source is inversely proportional to its voltage. In a second modexe2x80x94equal current, the two input power trains draw identical current from both sources, regardless of their voltage. An advantage with this mode is that currents are evenly distributed in the DC distribution system. Voltage transients are also minimized when the load current changes from two power sources to one.
The controllers can also be used to detect alarm signals by detecting over- or under-voltage or current.
In accordance with one preferred embodiment, a group of controllers are interconnected by a data link and are connected through that data link to a master controller (for controlling, for example, a shelf of circuit boards). Such master controllers, in turn, can be interconnected by another data link and connected to an office energy management controller for controlling an entire system.
Advantageously, communications among the control circuits can be used for passing alarm signals or balancing the load between the two power distribution systems, across collections of multiple boards, shelves or frames, and to respond to maintenance requests.
A problem of the type of power supplies illustrated in the preferred embodiment is that when a system or a board is started up, it is necessary to provide power to a board controller to bootstrap the main power system""s controller and other small loads on the board. In accordance with Applicants"" preferred embodiment this power supply is duplicated, each unit being connected to one of the two power distribution feeders. These power units, which typically supply only about 10 watts, have duplicated, isolated inputs and paralleled outputs, and are used to power the control unit.